Cardiac resynchronization therapy (CRT) is a treatment for heart failure patients in which one or more heart chambers are electrically stimulated (paced) to restore or improve heart chamber synchrony. Improved heart chamber synchrony is expected to improve hemodynamic performance of the heart, such as assessed by ventricular pressure and the rate of change in ventricular pressure or other hemodynamic parameters, thereby alleviating symptoms of heart failure. Achieving a positive clinical benefit from CRT is dependent on several therapy control parameters, such as the atrio-ventricular (AV) delay, inter-ventricular (VV) delay and pacing site(s). The AV delay controls the timing of ventricular pacing pulses relative to an atrial depolarization, intrinsic or paced. The VV delay controls the timing of a pacing pulse in one ventricle relative to a paced or intrinsic sensed event in the other ventricle. Pacing may be delivered in the right ventricle and/or the left ventricle.
Numerous methods for selecting optimal therapy parameters for delivering CRT pacing pulses have been proposed. For example, clinicians may select an optimal AV or VV delay using Doppler echocardiography or other imaging modalities to optimize a hemodynamic variable. Other methods may be based on a hemodynamic sensor signal or a sensor of mechanical heart function included in or coupled to the implantable medical device.
However, signals from mechanical sensors or imaging techniques may have a high degree of variability. For example, evaluation of mechanical ventricular dyssynchrony by echocardiographic methods may have both intra- and inter-operator variability. Moreover, signals from mechanical sensors may be influenced by several factors independent of CRT, such as dosage of medication, anesthetics for intraoperative evaluation, etc., which modulate the contractility and mechanical motion of the heart. Evaluation of signals from mechanical sensors often involve some method of signal averaging over multiple cardiac events and hence influenced by variations that may be present from one cardiac event to another, such as frequent ventricular ectopy interfering with CRT, which makes the effect of pacing alone difficult to isolate.
Analysis of multiple parameters detected from an implantable cardiac device for assessing heart failure projection is generally disclosed in pre-grant U.S. Publication No. 2012/0109244 (Anderson, et al.). The parameters may include mechanical synchrony, electrical synchrony, and/or electromechanical delay. A multi-polar lead is disclosed and may be used for acquiring signals for this analysis. The analysis may be the basis for modifying pacing delays (for example AV or VV delays) and thus are used to adjust the timing of pacing pulses but without consideration of pacing site. Pacing site selection for CRT is not addressed, yet pacing site selection may be critical to achieving positive patient response to CRT.